The roofing systems for commercial and industrial building roofs with low-slope roof decks typically include one or more layers of a low-density roofing insulation, a layer of roofing cover boards that overlie the low-density roofing insulation layer(s), and a waterproofing membrane that overlies the layer of cover boards. The layer(s) of low-density insulation, such as a low-density polymer-based foam insulation, if not protected, can be partially crushed or otherwise damaged from worker traffic over the insulation, the placement of heavy objects on the insulation, the weather, and other causes commonly encountered in roofing construction. The layer of roofing cover boards that overlies the one or more layers of low-density insulation, protects the more fragile low density insulation from damage, acts as a fire barrier, provides a suitable substrate for the attachment of the overlying waterproofing membrane, and augments the insulating function of the low-density insulation. The uppermost waterproofing membrane layer overlying the cover board layer protects the underlying cover board and insulation layers from moisture and other adverse climatic conditions. Normally, these three components (the low-density insulation boards, the roofing cover boards, and the waterproofing membrane) of the roofing system are separately manufactured and separately and successively applied to the low-slope roof deck.
Thus, roof cover board is typically used on top of roof insulation to provide a rigid, smooth top surface for the application of the membrane. It will protect the insulation from damages of foot traffic and give wind uplifting resistance and additional insulation to the roofing system. The application of cover board over mechanically attached insulation will also offer three other distinct advantages—(1) it reduces the shank length of the fastener, (2) it insulates the fastener/eliminating energy loss/possible thermal bridging at fasteners and insulation joints, and (3) it eliminates protrusions to the membrane surface from backed-out fasteners created by thermal contraction stress. The use of roof cover boards has become a standard method to enhance overall roof system performance for all low-slope roof systems.
Roof cover board currently on the market can be roughly divided into two categories—premium roof cover board and economical/entry level roof cover board. Premium roof cover board includes glass mat faced gypsum board (such as United States Gypsum Company's glass mat faced SECUROCK and Georgia Pacific's DENSDECK products) and fiber reinforced gypsum (such as United States Gypsum Company's gypsum-fiber SECUROCK, also known as “GF SECUROCK”). Entry level roof boards are primarily limited to wood fiber boards and perlite boards.
Premium roof cover board provides an excellent substrate for all types of conventional low-slope roofing membranes, particularly in fully adhered assemblies. The material is durable and provides superior impact and puncture resistance. However, this kind of cover board is normally heavy and expensive. Entry level roof cover board, on the other hand, does not have the quality of premium roof cover board, but is light weight and more affordable. Many builders and contractors prefer to use entry level roof cover board over premium roof board because of these two advantages. This is especially true for re-roofing applications.
Premium roof cover board includes glass mat faced gypsum board (such as USG's glass mat faced SECUROCK and Georgia Pacific's DENSDECK products) and fiber reinforced gypsum (such as USG's gypsum-fiber Securock). Entry level roof board includes primarily wood fiber board and Perlite Board. There is currently no gypsum fiber based light weight entry level roof cover board on the market.
U.S. Pat. Nos. 3,988,199, 4,126,512, 5,749,954, and 6,149,831 described formulations and manufacturing processes to make perlite boards. However, these formulations all have asphalt/bituminous material in them, either as internal additive or coating material to impart binding or water repellant properties to the perlite board. Asphalt is a highly combustible material and will significantly reduce the fire performance of the perlite board. In addition, Newsprint was used in the formulations to impart flexural strength. Newsprint (also known as “News”) is normally made with mechanical pulp or semi-mechanical pulp which has stiff and short cellulose fibers. Post-consumer Newsprint also contained a significant amount of ink which will work as a filler to lower the strength of the perlite board. Lastly, the amounts of starch used in these formulations are less than 5% of the total weight of solid materials in the formulation. This will result in a perlite board which is relatively weaker.
Gypsum fiber products, such as USG's GF SECUROCK, could be considered a heavy weight material. It is made using gypsum and cellulose fibers.